Osama Bin Laden's number two has called on the Islamist group Hamas to unite with al-Qaeda after its victory in Gaza over Fatah, in a web-posted audiotape.

Ayman al-Zawahiri also warned against any attempt by Arab countries to wrest control of the Gaza Strip from Hamas.

Al-Qaeda has in the past criticised Hamas for taking part in the political process in the Palestinian territories.

Hamas leaders, who espouse a more moderate brand of Islamist politics, have always shunned al-Qaeda advances.

The authenticity of the tape could not be immediately established, but it was posted on a website used by al-Qaeda-linked groups.

The speaker, identified as the Egyptian-born militant, called on Muslims around the world to back Hamas with arms, money and violence against US and Israeli interests.

The message was undated, but appeared to be a response to Hamas's rooting out of pro-Fatah security forces in Gaza 10 days ago.

'God's word'

The speaker urged Hamas to implement Islamic law in Gaza.

"Taking over power is not a goal but a means to implement God's word on earth," he said.

"Unite with mujahideen in Palestine... and with all mujahideen in the world in the face of the upcoming attack where Egyptians and Saudis are expected to play part of it," he added, suggesting the two Arab countries intend to intervene in Gaza.

"Provide them with money, do your best to get it there, break the siege imposed on them by crusaders and Arab leader traitors.

"Facilitate weapons smuggling from neighbouring countries. We can support them by targeting the crusader and Zionist interest wherever we can," he said in the 25-minute recording.